/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.core.io;

import java.io.IOException;
import java.io.InputStream;

/**
 * 一个在一定程度下能够代表{@link InputStream}的简单接口对象,他是{@link Resource}接口的基类.
 * 对于一次性使用的流,{@link InputStreamSource}能够用于所有给定的{@link InputStream}.
 * Spring的{@link ByteArrayResource} 或者任何基于文件的实现都能够最为一个具体的实例来使用.
 * 他允许多次读取底层内容的流.
 * 举例来说,他使得当前接口作为一个邮件附件的抽象内容源很有用.
 *
 * Simple interface for objects that are sources for an {@link InputStream}.
 * <p>
 * <p>This is the base interface for Spring's more extensive {@link Resource} interface.
 * <p>
 * <p>For single-use streams, {@link InputStreamResource} can be used for any
 * given {@code InputStream}. Spring's {@link ByteArrayResource} or any
 * file-based {@code Resource} implementation can be used as a concrete
 * instance, allowing one to read the underlying content stream multiple times.
 * This makes this interface useful as an abstract content source for mail
 * attachments, for example.
 *
 * @author Juergen Hoeller
 * @see java.io.InputStream
 * @see Resource
 * @see InputStreamResource
 * @see ByteArrayResource
 * @since 20.01.2004
 */
public interface InputStreamSource {
	/**
	 * InputStreamSource封装了任何能够返回InputStream的类,比如File,ClassPath下的资源以及ByteArray.
	 * 他只有一个 getInputStream方法,用来返回一个新的InputStream对象.
	 */


	/**
	 * 返回底层资源内容的输入流,且预期每一次调用都会创建一个新的流.
	 * 举例来说,当我们需要创建一个Java邮件这样的接口定义时,每一次打开都能够创建一个新的流就比较重要了,
	 * 因为这时候我们在创建邮件附件的时候,多次读取流.
	 * 所以,针对这种场景,每次调用getInputStream方法都会获得一个新的流.
	 *
	 * <p>
	 * Return an {@link InputStream} for the content of an underlying resource.
	 * <p>It is expected that each call creates a <i>fresh</i> stream.
	 * <p>This requirement is particularly important when you consider an API such
	 * as JavaMail, which needs to be able to read the stream multiple times when
	 * creating mail attachments. For such a use case, it is <i>required</i>
	 * that each {@code getInputStream()} call returns a fresh stream.
	 *
	 * @return the input stream for the underlying resource (must not be {@code null})
	 * @throws java.io.FileNotFoundException if the underlying resource doesn't exist
	 * @throws IOException                   if the content stream could not be opened
	 */
	InputStream getInputStream() throws IOException;

}
